Desensitization of ammonium perchlorate



United States Patent 3, 1 47, DESENSITIZATION This invention relates to a process for the desensitization of explosives containing ammonium perchlorate, and to compositions thus desensitized. Many explosives contain oxidizing salts as one of their components which are explosive. One class of such oxidizing salts is the monovalent chlorates, including perchlorates. Such chlorates are very sensitive to heat and explode readily under impact or friction, both of which generate heat, ammonium perchlorate being no exception. Thus it is hazardous to handle ammonium perchlorate.

It is believed that the high sensitivity of many explosives containing ammonium perchlorate is due to the sensitivity of ammonium perchlorate, it being the most sensitive of the components, or to the fact that it triggers the reaction due to its high oxidizing power.

It is an object of this invention to provide desensitized explosives containing ammonium perchlorate.

It is also an object of this invention to provide a desensitized form of ammonium perchlorate.

It is a further object of this invention to provide coated ammonium perchlorate wherein the coating agent and the ammonium perchlorate form a solid solution.

It is a further object of this invention to provide an easy and economical way to coat ammonium perchlorate crystals.

The above objects can be accomplished by coating the ammonium perchlorate crystals with certain'substances which can be crystallized under the same conditions as ammonium perchlorate because the crystal structures of the two materials are isomorphous.

Substances which are-isomorphous with ammonium perchlorate which are not strong oxidizers themselves are sulfates, fluoroborates, and certain compounds of gold, cesium, radium, and thallium. Those which are best suited for the purposes of this invention, however, are the fluoroborates, though the invention is not limited to such substances.

Of the fiuoroborates the preferred one is ammonium fluoroborate as will be seen from data presented later.

The coating of ammonium perchlorate is best accomplished by very slowly adding a saturated solution of ammonium fluoroborate to solid ammonium perchlorate crystals with thorough mixing, for example, in a rotating drum. The water thus added evaporates very rapidly so that there is little solution of ammonium perchlorate as the overgrowths are formed. The thickness of the ammonium fluoroborate coating need not be great, uniform, or even complete to produce good desensitization. It is important to break up aggregates of ammonium perchlorate during the coating as they are formed since they could break up on mixing the ammonium perchlorate in a composition, leaving undesensitized faces.

The coating of ammonium perchlorate is also accomplished by simultaneous crystallization of ammonium perchlorate and ammonium fluoroborate. Saturated solutions of the two salts at room temperature (2030 C.) are mixed. The water in the mixed solution is evaporated while the solution is agitated, resulting in crystallization. The evaporation can be speeded by gentle warming of the solution or by reducing the pressure over the solution. The crystallization process can be initiated a little sooner by seeding with ammonium perchlorate 3,147,160 Patented Sept. -1, 1964 crystals. The evaporation is carried on until a thick slurry results; then the crystals are manually removed. Mixed crystals of ammonium perchlorate and ammonium fluoroborate result from this crystallization with ammonium fluoroborate tending to accumulate at the outer surfaces due to differences in solubility and concentration.

Another form of the process involves the use of hydrofluoroboric acid. Crystals of ammonium perchlorate are wetted by slowly adding the acid to the ammonium perchlorate crystals while thoroughly mixing the mixture, for example, in a rotating drum. When thoroughly wet, the crystals are exposed to excess ammonia at room temperature for up to two hours. An overgrowth of ammonium fluoroborate is formed according to the reaction:

Alternatively, the wetted crystals are treated with concentrated ammonium hydroxide added very slowly so that water formed in the reaction is evaporated about as quickly as it is formed. The reaction is Another process involves the sublimation of ammonium fluoroborate. This compound is placed in a vessel where the pressure is lowered and the temperature is raised, causing the material to vaporize. This vapor is led to another cooler vessel where it solidifies upon crystals of ammonium perchlorate in the vessel.

The foregoing has been concerned with the coating of amomnium perchlorate prior to mixing in a composition but the whole explosive mixture containing ammonium perchlorate can be treated according to the first and third enumerated methods to produce desensitization. The ammonium perchlorate becomes coated along with the other components, however, this does not affect the energy output of the mixture appreciably.

According to the present method, crystals of ammonium perchlorate are coated with a substance which forms a zoneof solid solution with the crystals, said zone being covered by another zone of a crystallized inert substance. Thusa continuous crystalline structure exists from the center of an ammonium perchlorate crystal to the outer boundary of the inert coating upon the crystal.

Such a coating is sufficiently strong to prevent its being broken in handling operations, yet the coating will easily crack and expose perchlorate surfaces when detonated so as not to interfere with the explosiveness of the ammonium perchlorate. i

The tabulation of test data below shows the eflect of ammonium fluoroborate on thesensitivity of ammonium perchlorate.

Mixture 50% Point,

0% by wt. ammonium fluoroborate on ammonium perchlorate 40 6% by wt. ammonium fluoroborate on ammonium perehlora to 73 10% by wt. ammonium fluoroborate on ammonium perchlorate 77 20% by wt. ammonium fluoroborate on ammonium per- 0 rate 82 3 content of as little as six percent almost doubles the height of the 50 percent point; this is approximately the same effect produced by the addition of 20 percent ammonium fluoroborate, so the most useful percentage of ammonium fluoroborate is from four to percent by weight.

The preferred fluoroborate is the ammonium salt. The tabulation of test results given below illustrates the effect of the varying amounts of different fluoroborates on DXY, an ammonium perchlorate containing explosive. DXY contains by weight about 50 percent ammonium perchlorate, 25 percent aluminum, 18 percent TNT, seven percent RDX. RDX is trinitrotrimethylenetriamine, 2 2)3 3( z)s- The ammonium salt gives the best desensitization as can be seen from the above results.

Ammonium fluoroborate is operable as a desensitizer of an explosive containing ammonium perchlorate over a wide range, from almost zero to 17 percent and the percentage of ammonium fluoroborate could be increased much more with added desensitization. The most useful range appears to be from five to 11 percent by weight.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. The process of desensitizing ammonium perchlorate which comprises coating crystals thereof with an overgrowth of a fluoroborate salt of ammonium and alkali metals.

2. The process of claim 1 whereby the coating is accomplished by slowly adding a saturated solution of the fluoroborate salt to the crystals with thorough mixing.

3. The process of claim 1 whereby the coating is accomplished by mixing saturated solutions of ammonium perchlorate and the fluoroborate salt, and slowly evaporating the water from the mixed solution whereby the ammonium perchlorate crystallizes out first and the fluoroborate salt crystallizes on the ammonium perchlorate crystals.

4. The process of claim 1 whereby the coating is accomplished by wetting the ammonium perchlorate crystals with hydrofluoroboric acid and then treating the crystals with a compound selected from the class consisting of ammonia, ammonium hydroxide, and alkali metal hydroxides.

5. The process of claim 1 whereby the coating is accomplished by subliming the fluoroborate salt and condensing it on crystals of ammonium perchlorate.

6. The process of desensitizing ammonium perchloratecontaining explosives comprising the steps of coating crystals of the perchlorate with an overgrowth of a fluoroborate salt of ammonium and alkali metals, and incorporating the coated crystals in an explosive mixture.

7. The process of desensitizing ammonium perchloratecontaining explosives comprising the steps of dividing the explosive into small particles, and coating the particles with an overgrowth of a fluoroborate salt of ammonium and alkali metals.

8. A composition of matter consisting essentially of ammonium perchlorate and an overgrowth of a fluoroborate salt of ammonium and alkali metals, said fluoroborate salt comprising from about one to about 20 percent by weight of the ammonium perchlorate.

9. The composition of claim 8 in which the salt is ammonium fluoroborate and the overgrowth comprises from about four to about 10 percent by weight of the ammonium perchlorate.

10. The composition of claim 8 in which the ammonium perchlorate is a crystal and in which a continuous crystalline structure exists from the center of the crystal to the outer boundary of the overgrowth.

11. A composition of matter consisting essentially of an ammonium perchlorate-containing explosive in which ammonium perchlorate crystals are coated with an overgrowth comprising from about one to about 17 percent by weight of fluoroborate salt of ammonium and alkali metals.

12. The composition of claim 11 in which the salt is ammonium fluoroborate and the overgrowth comprises from about four to about 10 percent by weight of the ammonium perchlorate.

References Cited in the file of this patent UNITED STATES PATENTS 1,276,537 Johnson Aug. 20, 1918 FOREIGN PATENTS 14,866 Great Britain 1915 OTHER REFERENCES Buckley: Crystal Growth, 1951, pp. 35, 96, 402, 412. (Copy obtained from Scientific Library.

Schulz: Acta Crystallographica, vol. 5, 1952, pages 264-265. 

11. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF AN AMMONIUM PERCHLORATE-CONTAINING EXPLOSIVE IN WHICH AMMONIUM PERCHLORATE CRYSTALS ARE COATED WITH AN OVERGROWTH COMPRISING FROM ABOUT ONE TO ABOUT 17 PERCENT BY WEIGHT OF FLUOROBORATE SALT OF AMMONIUM AND ALKALI METALS. 